1. Field of the Invention
The present invention relates to a data transmission system using a human body as a signal path, and more particularly to a system composed of a first transceiver adapted in use to be worn on a human body and a second transceiver adapted to be connected to an associated equipment which utilize data transmitted from the first transceiver.
2. Description of the Prior Art
U.S. Pat. No. 4,591,854 discloses a data transmission system using the human body as a signal path. The system includes a portable transmitter in the form of a wrist watch to be worn on a user, and a control unit or signal receiver. The transmitter has a pair of electrodes on the back of the wrist watch for direct contact with the skin of the user. One electrode acts as a signal electrode which is connected through a portion of the user""s body to a touch electrode of the signal receiver, while the other electrode acts as a ground electrode which is coupled through or not through the other portion of the user""s body to a circuit ground of the signal receiver to complete a signal path through the user""s body for data transmission from the wrist watch to the signal receiver. The signal receiver includes a touch sensor to detect touching state and non-touching state of the touch electrode so as to enable the signal receiver to receive the data from the wrist watch when the touching is detected for the purpose of avoiding accidental enabling of equipment connected to the signal receiver by radiated signals. To enable this automatic reception of the data at the signal receiver, the wrist watch has to be always ready for transmitting the data or has to include a manual start switch for starting transmission of data. When the wrist watch is designed to be constantly energized to be always ready for the data transmission, a battery energizing electronic components of the wrist watch is likely to be soon exhausted. When the wrist watch is designed to include the start switch, it adds a cumbersome manual operation, thereby detracting from the touch-responsive data transmission.
In view of the insufficiencies, the present invention has been achieved to provide a touch-responsive data transmission system which is capable of elongating the battery life of the transceiver worn on the user""s body yet assuring one-touch data transmission. The system in accordance with the present invention comprises a first transceiver adapted in use to be worn on the user""s body and a second transceiver adapted to be connected to an associated equipment which utilizes data transmitted from the first transceiver. The first transceiver comprises a battery energizing the circuit of the first transceiver, a ground electrode for direct contact with the user""s body to establishing an electrical connection through the user""s body to a ground, and a signal electrode spaced from the ground electrode for direct contact with the user""s body. Also, the first transceiver includes a data memory storing first data to be transmitted, a first modulator which is energized selectively by the battery for converting the first data into a first modulated voltage signal, and a first signal transmitter which is energized selectively by the battery to apply the first modulated voltage signal across the signal electrode and the ground electrode. Further included in the first transceiver are a start signal detector which is constantly energized by the battery for detection of a start signal received through the signal electrode, and a first controller which is constantly energized by the battery and is connected to the start signal detector so as to energize the first modulator and the first transceiver for applying the first modulated signal in response to the start signal.
The second transceiver comprises a second circuit ground for connection with the ground, a single touch electrode for direct contact with a portion of the use""s body wearing the first transceiver, a second signal detector connected across the touch electrode and the second circuit ground to detect the first modulated voltage signal, and a second demodulator for converting the first demodulated signal back into the first data. Also, the second transceiver includes a start signal generator which generates the start signal and provides it through the touch electrode, and a touch sensor which is connected to the touch electrode to give a touch signal when the touch electrode is touched by the user""s body. Further included in the second transceiver is a second controller which energizes the start signal generator to provide the start signal upon receiving the touch signal, thereby enabling data transmission from the first transceiver to the second transceiver. Thus, the first signal transmitter and the first modulator of the first transceiver can be kept deenergized until the user touches the touch electrode of the second transceiver, thereby saving energy during non-operated condition and assuring a prolonged battery life of the first transceiver. Also, the transmission of the first data can be made automatically simply by touching the touch electrode and without requiring any additional starting procedure. This is particularly advantageous in a case where the first transceiver is realized in the form of a battery operated wrist watch for use in a keyless entry system for access to a vehicle, restricted equipment, and restricted area.
Preferably, the second transceiver further includes a second modulator for converting second data into a second modulated voltage signal which is applied between the touch electrode and the second circuit ground for bilateral data transmission between the first and second transceivers. To receive the second data from the second transceiver, the first transceiver includes a first demodulator for converting the second modulated signal, which is detected through the signal electrode, into the second data. Further, the first controller has a function of modifying the first data in accordance with the second data. This arrangement is advantageous when the present system is utilized in an automated gate which permits the entry of a person wearing the first transceiver at a certain charge or fare. Thus, each time the person passes through the gate, the fee determined by the second data is subtracted from a credit stored as the first data of the first transceiver for updating the first data by the second data.
It is preferred that that first signal transmitter includes a current regulator which keeps a current flowing between the signal electrode and the ground electrode substantially at a fixed level for the purpose of successfully making reliable data transmission irrespective of differing electrical resistance of differing portions of the skin in contact with the signal and ground electrodes.
At least one of the signal electrode, the ground electrode, and the touch electrode may be coated with an insulation layer for making capacitive coupling with the user""s body, avoiding the occurrence of electrical double layer at the interface between the user""s skin and the electrode which would cause electrical polarization, the source of undesired noise.
The second circuit ground may be connected to the ground through a ground line for reducing impedance between the second circuit ground and the ground to which the ground electrode is connected through the user""s body.
Also, the second transceiver is preferred to have an electrically conductive chassis to which the second circuit ground is connected.
Further, the second circuit ground may be connected to an electrically conductive sheet which is adapted to be installed on a site such that the human body wearing the first transceiver stands on the conductive sheet. Thus, it is possible to reduce the impedance between the second circuit ground and the user""s body for reliable data transmission from the first transceiver to the second transceiver through the user""s body.
The first transceiver may additionally include a display for indication of the first data so that the user can check the data. The data memory of the first transceiver may be detachable to the first transceiver so that the data memory can be installed on a separate writer for rewriting the first data or can be replaced with another data memory.
The first transceiver is held on a disk with the signal electrode and the ground electrode being arranged on one face of the disk. Thus, the first transceiver can be readily incorporated into a wrist watch with the disk forming the back plate of the watch.
Alternately, the first transceiver may be held on a ring with the signal electrode and the ground electrode being arranged on an interior face of the ring. Thus, the first transceiver can be easy to be carried on the user as well.
The second transceiver may be configured such that the touch sensor and the second controller are constantly energized by a power source to be always read for operation, while the second signal detector and the second demodulator are selectively energized by the power source. The second controller is responsive to the touch signal to energize the second signal detector and the second demodulator. Thus, the second signal detector and the second demodulator are kept deenergized until the second controller receives the touch signal for saving the power while the second transceiver is non-operating condition of not receiving the first data from the first transceiver.
In addition, the second controller has a function of deenergizing the second signal detector and the second demodulator after deriving the first data. More preferably, the second controller is configured to provide a predetermined time period for receiving the first demodulated voltage signal and to deenergize the second signal detector and the second demodulator after the elapse of the predetermined time period.
These and still other objects and advantageous features of the present invention will become more apparent from the following description of the preferred embodiments when taken in conjunction with the attached drawings.